Dual poppet pressure relief valve with vacuum adaptor capability

ABSTRACT

A pressure relief valve is disclosed with a first stage valve that is in series with a second stage valve, with an enclosed cavity between the first stage valve and the second stage valve. The first stage valve relieves pressure from an enclosure into the enclosed cavity between the stages, when the pressure is above a cracking pressure of the first stage valve. The second stage relieves pressure from the enclosed cavity when the pressure is above the cracking pressure of the second stage valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of priorco-pending U.S. Provisional Patent Application No. 62/792,739, filedJan. 15, 2019, the disclosure of which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to a dual poppet pressure relief valve withvacuum adaptor capability.

BACKGROUND

For various reasons, a pressure differential may be formed between aninternal pressure inside of a sealed enclosure and an external pressureoutside of the enclosure (such as a subsea housing). A Pressure ReliefValve (PRV) can be used on the sealed enclosure to prevent the internalpressure from becoming significantly higher than the external pressure.For safety reasons, the internal pressure should not becomesignificantly higher than the external pressure.

For example, in the subsea industry pressure relief valves withrelatively low cracking pressures are often used as a safety device toprevent the buildup of inside pressure within a subsea electronicshousing. Subsea housings are hydrostatic pressure vessels designed forexternal pressure and are typically not capable of withstanding evenmodest relative internal pressure without failure. Significant internalpressures can develop as the result of hydraulic leaks, batteryoff-gassing and or slow sea water leaks that cannot relieve internalpressure quickly enough during recovery to the surface.

Unfortunately pressure relief valves have a reputation for poorreliability in the subsea environment. Corrosion and fouling of themoving parts by suspended particulate matter can sometimes lead tofailure by preventing the valve from reseating sufficiently to establisha reliable seal. While the use of redundant corrosion resistantmaterials and seals improve reliability of subsea pressure relief valvesthese enhancements do not address the fundamental problem of themechanical parts within the valve; each being single point of failure.

In prior implementations, a PRV can include a valve body, a poppet thatseals on the valve body, a spring that encourages the poppet to stay incontact with the valve body to maintain a seal, and a nut the holds thespring in place. The seal of the PRV on the poppet may permit egress ofthe internal pressure without allowing the ingress of externalenvironment (such as seawater), as this could destroy valuable equipmentresiding internal to the sealed enclosure. However, even a single pieceof debris may become lodged within a sealing area of prior PRVs, leadingto potentially catastrophic single point failure.

There is often need to be able to evacuate the sealed enclosure and/orbackfill the sealed enclosure with a gas or liquid, and do to allowventing, evacuation, and/or backfill to occur with higher reliabilityand without risk of single point failure.

SUMMARY

This section provides a general summary of the present disclosure and isnot a comprehensive disclosure of its full scope or all of its features,aspects, and objectives. For purposes of this application, certain termsmay be considered interchangeable; for example, the terms “internalpoppet,” “first stage valve,” “first poppet,” and “first poppet valve”may be used interchangeably, and the terms, “external poppet,” “secondstage valve,” “second poppet,” and “second poppet valve” may be usedinterchangeably.

The embodiments of the pressure relief valves disclosed relate topressure relief valves for relieving pressure inside a chamber,including a chamber used in the deep sea or other high pressureenvironments with improved reliability over existing pressure reliefvalve designs. In an example embodiment, the relief valve includes afirst stage with a first valve having a first cracking pressure value,and a second stage with a second valve, having a second crackingpressure value. An enclosed cavity is between the first stage and thesecond stage, so that the first valve relieves pressure above the firstcracking pressure value from an enclosed housing into the enclosedcavity, and the second stage valve relieves pressure above the secondcracking pressure value from the enclosed cavity into an outsideenvironment. In one exemplary embodiment, the second cracking pressurevalue is approximately 3-4 psi greater than the first cracking pressurevalue, but may comprise any desired range.

The first valve may include a first body or first housing and a firstpoppet, and the second valve may include a second body or second housingand a second poppet. The first body may have an opening configured toreceive the second body, with the second body occupying at least aportion of the opening. At least one seal may be placed between thefirst body and the second body. The enclosed cavity may be formed with asealed space between the first body and second body.

The second valve may also include a threaded stem and a second stagespring configured to bias the second valve into a closed position untila sufficient opening force is applied to the valve or sufficientinternal pressure builds within the cavity. An adjustment nut may beused to adjust a load on the first stage spring and a second stagespring (or both), and may allow selective bias between closing forcesapplied to the first poppet and second poppet. In various embodiments,the adjustment nut is positioned on the threaded stem of the secondpoppet to set the cracking pressure values as desired.

The adjustment nut may be set so that the first cracking pressure valueis higher than the second cracking pressure value. Alternatively, thefirst cracking pressure value may be approximately the same as thesecond cracking pressure value. In another embodiment, the firstadjustment nut may be set so that the first cracking pressure value islower than the second cracking pressure value.

The first adjustment nut may be set so the first cracking pressure isapproximately within a first range. The range may be any desired valuesto allow mechanical progression between opening of the first poppet andthe second poppet, for example 3-4 psi, 5-7 psi, or 5-10 psi. The secondpoppet valve may include a second spring configured to keep the secondpoppet valve in a closed position until the valve is actuated from anexterior tool or from internal pressure buildup within the cavity.

A cap may be placed next to the second valve to prevent particles fromentering the second valve. The cap may be attached to the second body ina manner so that the cap will be removed if a high rate of fluid passesthrough the second valve.

A high flow indicator may be attached to the second stage. The high flowindicator may be configured to indicate when a high flow of fluid haspassed through the second valve.

The first poppet valve may include a bottom sealing surface, a verticalbore, and a horizontal bore passing through the vertical bore configuredto accept a locking pin. A first valve spring disposed around a verticalflange of the first poppet valve may apply a bias to the first poppet toremain in a closed position until sufficient forces are applied to thesecond poppet to apply lifting forces to the locking pin disposed withinthe horizontal bore. The first valve spring may be configured to entrapthe pin within the horizontal bore once the spring is installed over theflange.

In another example embodiment, an enclosed housing may have an exteriorand an interior, where the enclosed housing is configured to protect theinterior from pressurized fluids on the exterior of the enclosedhousing. The enclosed housing may also include a pressure relief portthat allows fluid to pass from the interior of the enclosed housing tothe exterior of the enclosed housing. The enclosed housing may include apressure relief valve having a total cracking pressure value. Thepressure relief valve may be fixed in the pressure relief port that isconfigured to allow fluid to pass in one direction from the interior ofthe enclosed housing to the exterior of the enclosed housing when fluidpressure on the interior of the enclosed housing is greater than the sumof fluid pressure on the exterior of the housing and the total crackingpressure value. The pressure relief valve may include a first stagevalve, and a second stage valve, and an enclosed cavity between thefirst stage valve and the second stage valve.

The first stage valve may have a first cracking pressure value, and thesecond stage valve may have a second cracking pressure value that islower than the first cracking pressure value. The first stage valve maybe configured to allow fluid to pass in one direction from the interiorof the housing into the enclosed cavity. The second stage valve may beconfigured to allow fluid to pass in one direction from the enclosedcavity to the exterior of the housing. The enclosed housing may beconfigured to withstand fluid pressure, with a maximum fluid pressure upto the design operating pressure.

An example method of producing a high reliability pressure relief valvemay include the steps of: assembling a first stage with a first pressurerelief valve for relieving fluid pressure from an enclosed housing abovea first cracking pressure value; assembling a second stage with a secondpressure relief valve to relieve pressure above a second crackingpressure value; and assembling the first stage with the second stage inseries, with an enclosed cavity between the first stage and the secondstage, where the first stage relieves pressure above the first crackingpressure value from the enclosed housing into the enclosed cavity, andwhere the second stage relieves pressure above the second crackingpressure value from the enclosed cavity into an outside environmentoutside the enclosed housing. The first cracking pressure value may be ahigher pressure than the second cracking pressure value. The examplemethod may include the steps of: adjusting the first stage to set thefirst cracking pressure value; and adjusting the second stage to set thesecond cracking pressure value. The example method may further includedisposing a valve adjustment nut on a threaded portion of the secondpoppet valve to accept a first spring and second spring, the firstspring applying bias-closed force to the first poppet valve, and thesecond spring applying bias-closed force to the second poppet valve. Theexample method may also include adjusting the nut to apply selectedfirst and second cracking force ranges respectively to the first andsecond poppet valves.

As will be made clear, the disclosed embodiments of the pressure reliefvalve provide important advantages in providing a highly reliablepressure relief system for enclosed housings in a high pressureenvironment. Disclosed herein are implementations of a pressure reliefvalve (PRV) comprising a first poppet and a second poppet. The firstpoppet and the second poppet can be packaged as one unit and work inseries.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detaileddescription when read in conjunction with the accompanying drawings. Itis emphasized that, according to common practice, the various featuresof the drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.

FIG. 1A is a plan view of a dual poppet PRV assembly in accordance withaspects of the present disclosure.

FIGS. 1B and 1C are a perspective views of a dual poppet PRV assembly inaccordance with aspects of the present disclosure.

FIG. 2A is a cross sectional view of the dual poppet assembly of FIG. 1Ain accordance with aspects of the present disclosure.

FIG. 2B is another cross sectional view of the tooling for the dualpoppet assembly of FIG. 1A in accordance with aspects of the presentdisclosure, axially rotated approximately 90 degrees from FIG. 2A.

FIG. 2C is an enlarged view of a portion of FIG. 2A, showing a gapdisposed between a locking pin and an internal bore of the second stagevalve.

FIG. 3 is a cross sectional view of the dual poppet assembly functioningin accordance with aspects of the present disclosure.

FIG. 4A is an external poppet assembly in accordance with aspects of thepresent disclosure showing a second poppet seated in a second stagebody/housing.

FIG. 4B is an internal and an external poppet in accordance with aspectsof the present disclosure.

FIG. 5 is a cross sectional view of a portion the dual poppet PRV inaccordance with aspects of the present disclosure, illustratinginstallation and entrapment of a locking pin.

FIG. 6 is a perspective view of a valve adjustment nut of the presentinvention.

FIG. 7 is a top perspective view of a first poppet valve of the presentinvention.

FIG. 8 is a top perspective view of a first valve housing/body of thepresent invention.

FIG. 9 is a perspective view of a second poppet valve of the presentinvention.

FIG. 10 is a perspective view of a second valve housing/body of thepresent invention.

Identical reference numerals between figures indicates like or similarcomponents.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the disclosure in its application or uses. Forpurposes of clarity, the same reference numbers are used in thedescription and drawings to identify similar elements.

To improve reliability of the seal of the PRV on the poppet inpermitting egress of the internal pressure without allowing the ingressof external media (such as seawater), two independently operating PRVsarranged in series, can be placed in a single valve body. Thereby, ifone PRV fails the other will protect the equipment internal to theenclosure, such as a sealed enclosure.

A secondary use of the PRV can be as a conduit to pull a vacuum insidethe enclosure (such as a subsea housing in preparation to deploy). Thevacuum can provide confirmation that all seals are functioning.

A third use of the PRV can be used as a conduit to allow back-fill witha gas or liquid. On a single poppet PRV, an adaptor can manually liftthe poppet and expose a flow path for these procedures.

A fourth use of the PRV can be used as a scuttle valve that is to forcethe valve open mechanically to allow the external media to flood theinternals of the enclosure. This may be used in subsea applications toallow seawater inside the enclosure, which could render the internalequipment unusable.

FIGS. 1A-1C illustrate external views of a dual PRV assembly. A dual PRVmay be referred to as a dual poppet relief valve or a dual poppet PRV.The dual PRV can include two poppets in series, including a first poppet(or internal poppet) and a second poppet (or external poppet). Thepoppets as referred to in this disclosure can be any devices that canopen and close flow of a valve seat. The poppets can be formed into anydesired shape. The poppets can be formed from any desired material, forexample steel, aluminum, or in preferred embodiments, titanium.

FIGS. 2A and 2B show, in cross section, an example arrangement of a dualPRV of the present invention. A first stage valve 211 is disposed nearan orifice 212B, in the first housing or first body 212. The first stagevalve 211 of sealably engages a bottom surface of the first housing 212,and with first seal 216, blocks free fluid communication from aninterior area through orifice 212B. First date valve 211 is mechanicallycoupled to the second stage valve 221 through a pin 258 disposed withinbore 221E of the second stage valve, and the horizontal bore 211D of thefirst stage valve. First stage spring 214 is coupled between a flange offirst stage valve 211 and the adjustment nut 268, and biases the firststage valve into a closed position. Second stage spring 224 is coupledbetween the adjustment nut 268 and the second housing 278, and biasesthe second stage valve into a closed position. Adjustment of the nut 268allows differential forces to be applied between the first date valvesecond stage valve, thus allowing cracking forces to be selected foreach valve. The adjustment nut 268 is shown disposed on a threadedportion 221G of the shaft 221C of the second stage valve 221, andadditional detail of the second stage valve may be seen as shown in FIG.9 . A second valve seal, 226 is disposed within a bottom cavity of thesecond stage valve 221 and provide sealing between a bottom surface 221Bsecond stage valve 221 and the second body 278. A bore 221E ishorizontally disposed in a distal end 221F the second stage valve 221,and is disposed to accept a locking pin 258, so that external pullingforces applied to the second stage valve may be coupled through thelocking pin 258 to the first stage valve 211. As shown in FIG. 2C,dimensions of the bore 221E and the locking pin 258 are selected tocreate a desired a gap 277. The dual poppet PRV can include a 288retainer formed of nylon, or other desired material, positioned in anupper portion (e.g., FIG. 8, 212C) of the dual poppet PRV. All parts inthe foregoing example which are exposed to sea water may be Titanium,coated to reduce galvanic corrosion.

On a dual PRV, the external poppet may be physically accessible to liftand the second poppet may prevent the vacuum operation. Because thevalves should operate independently to be viable as double protection,it may not be feasible to make a fixed connection between the twopoppets.

Issues may arise when the two poppets to operate independently duringoperation. For example, both poppets may not lift during the vacuumoperation. Embodiments of the present disclosure provides a solution bycreating a coupling between the two poppets (achieved, as describedabove in regards to FIGS. 2A-2C by the locking pin 258 disposed withinbores 221E of the second poppet and bore 211D of the first poppet) thatcan have more clearance than required during relief operation, thusallowing the poppets to work independently. However, the clearance (FIG.2C, 277 ) in the coupling can be small enough to be closed when manuallylifting the external poppet, thereby also lifting the internal poppet;this can complete the conduit and allow for the vacuum/backfillingprocess.

Further embodiments also provide that, the coupling between the twopoppets may not be restricted during operation. Rather, the coupling canbe manually moved enough to influence the internal poppet with theexternal poppet. The coupling can be configured to allow for calibrationof each PRV and then connect them in a simple, reliable way. Theexternal poppet can attach to an external device to mechanically liftthe external poppet, which in turn can also lift the internal poppet.

As illustrated in FIGS. 2A-C, an end 221F of the external poppet 221 canbe extended in a shaft-like fashion (e.g. threaded stem 221C). Thisshaft can slide into a bore 211C on the internal poppet 211, allowingindependent movement of both the internal poppet and the externalpoppet. The sliding can be performed in a concentric fashion or anyother desirable way. Both an external poppet shaft and an internalpoppet bore can receive a cross-bore hole. As shown in FIG. 5 , thecoupling can be formed by sliding a locking pin 258 through thecross-bore that limits the (relative) axial movement between the twopoppets. Because independent axial movement may be required foroperation, the pin 258 and bores 221E/211D can be configured forsufficient clearance. The clearance may be configured to include a largeenough manual movement (lifting) of the external poppet to close the gapand begin lifting the internal poppet 211. The pin 258 can be relativelyloose to allow for independent poppet operation. The pin can also betrapped from falling out by an internal PRV spring. The locking pin 258can be formed of nylon, PRV thread lock material, or any other desiredmaterial. The pin 258 can be positioned in a lower portion of the dualpoppet PRV. Also as shown in FIG. 5 , the locking pin 258 can beinserted into the bore 211D/221E by lifting the first stage spring 268and sliding the pin 258 into the desired position or any other desiredinsertion method. After the pin 258 is positioned, the spring 214 can bereleased. When the spring is released, the pin may be entrapped by thespring 214 and remain in place.

In one exemplary embodiment, the pressure relief valve (PRV) includes afirst poppet and a second poppet. The first poppet and the second poppetare packaged as one unit and work in series. The PRV can be configuredto operate at extreme external pressures (such as in the deepest oceanat depths or other external pressure environments). For example, theexternal pressures in the ocean may include pressures at depths of 6,000meters or greater.

The dual poppet PRV can include external features that interface with anadaptor and allow the PRV to be opened for evacuation and backfillingoperations of the enclosure (e.g., a vacuum adaptor, a sealedenclosure). The dual poppet PRV can have an internal coupling betweenthe two poppets that do not prevent independent operation of thepoppets. The internal coupling between the two poppets can allow theinternal poppet to be manually lifted by the external poppet. Theinternal coupling between the two poppets can use a sliding fit, or anyother desired fit, that keeps the two poppets relatively concentric. Theinternal coupling between the two poppets can have a pin, such as across pin, or any other desired device, which limits the axial relativemovement of the two poppets, allowing the external poppet to lift theinternal poppet. The internal coupling between the two poppets can havethe pin, such as the cross pin that does not inhibit the axial, relativemovement, or any other desired movement, of the two poppets duringoperation. The internal coupling between the two poppets can have thepin, such as the cross pin, which is retained by the internal poppetspring.

The example configuration shown in FIGS. 2-4 shows an adjustment nut 268for adjusting the cracking pressure of the first and second poppetvalves. A perspective view of the nut 268 is shown on FIG. 6 , andincludes a flanged portion 268B to engage and retain the first stagespring 214, and flat surfaces 268B to allow the nut to be more easilyturned on threaded shaft 221G (see also FIG. 9 ), and to allow fluidcommunication between an external area proximate the opening 212A andinternal area proximate the opening 212B. The internal bore of the nut268B is typically threaded to engage with threads 221G (FIG. 9 ) of theshaft 221C, although threads are not show in FIG. 6 for simplicity. Inother embodiments other means may be used to set a cracking pressure,which may be adjustable, or alternatively may be set without adjustment.Further, one or both of the valves may have an adjustment available forthe cracking pressure.

FIG. 3 illustrates one mode of operation of the dual PRV of the presentinvention. In this mode, a force 310 is applied to the second poppet 212to pull to poppet 212 toward the external opening 212A area. Such forcemay be applied through a tool traded into the bore 221D as show in FIG.9 . The second poppet 221 moves toward the external direction, couplingto the first poppet through installed locking pin 268. Once sufficientforce is applied to bias the first and second poppets into an openposition, fluid communication may occur from, for example, an internalarea 312 passing through opening 212B, around 313 the now-open seal 216of the first poppet 211, into the enclosed cavity 212D up 314 theenclosed cavity around the adjustment nut 268 (especially around flatportions 268B that allow fluid communication) and shaft 221C and through316 the now-open area appearing between the seal 226 and the secondhousing surface 278A. Releasing the force 310 will allow both valves totranslate to a closed position through the spring forces of springs 224,214.

FIG. 10 illustrates a perspective view of a second housing/body 278 ofthe present invention, where the second poppet 221 may be seated in area278A, and stem 221C may pass through opening 278B to the cavity formedbelow once the part is installed. Grooves 278C are configured to providemechanical coupling between the first housing 212 and the second housing278, and the coupling is illustrated in FIGS. 2A-2B.

In the embodiments shown and discussed, particular configurations areshown by way of example, and other configurations and devices may beused within the disclosed novel inventive concepts. For example, theshape and configuration of the first body 212 and the second body 278are shown by way of example. In alternative embodiments, the first bodyand the second body may be formed together rather than as two separateparts. Similarly, the type and configuration of the valve mechanisms maybe any valve mechanism that allows a set cracking pressure and iscapable of allowing fluid to flow in one direction, and withstandoutside pressure. The drawings also show multiple redundant seals by wayof example and not limitation. The invention may be practiced with anynumber of redundant seals sufficient to prevent fluid from passing fromthe exterior of the housing into the interior 212B of the housing 212.

In the example embodiments, springs are discussed and illustrated ascoil springs, such as metal corrosion resistant material springs. Othersprings may be used to provide force to keep the valve closed below thedesired cracking pressure. A spring is any elastic object used to storemechanical energy.

The valve and housing discussed above may be used in a high pressureenvironment, such as in a deep sea environment. The fluid inside thehousing may be air, or alternatively, it may be other fluids. The fluidoutside the housing may be water, for example seawater, or it may be airor other fluids.

The example illustrated configurations shows an adjustment nut 268 foradjusting the cracking pressure of the valves. In other embodimentsother means may be used to set a cracking pressure, which may beadjustable, or alternatively may be set without adjustment. Further, oneor both of the valves may have an adjustment available for the crackingpressure.

The examples discussed above have described relieving pressure frominside a housing as an example application of the pressure relief valve.This is not by way of limitation as the pressure relief valve 100 may beused in any environment where fluids are to be controlled and allowed toflow in only one direction based on pressure differentials. The valvedisclosed may allow fluid into a normally high pressure system when thepressure drops below a set value, such as in a water or gas supplysystem, and may be used for other applications other than those wherepressure is relieved. In this manner an outside, external or exteriorenvironment is describing the environment where fluid flows after thefluid passes through the second stage of the valve, and an inside,internal, or interior environment is describing the environment fromwhich fluid will flow into the valve when the pressure differentialallows the valve to open.

While the principles of the invention have been made clear inillustrative embodiments, there will be immediately obvious to thoseskilled in the art many modifications of structure, arrangement,proportions, and methods, the elements, materials, and components usedin the practice of the invention, and otherwise, which are particularlyadapted to specific environments and operative requirements withoutdeparting from those principles. The appended claims are intended tocover and embrace any and all such modifications, within the limits onlyof the true spirit and scope of the invention.

While the disclosure has been described in connection with certainembodiments, it is to be understood that the disclosure is not to belimited to the disclosed embodiments but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims, which scope is to be accordedthe broadest interpretation so as to encompass all such modificationsand equivalent structures as is permitted under the law.

1-11. (canceled)
 12. A pressure relief valve (PRV) assembly comprising:a housing having an opening therein, an interior cavity, and apassageway extending between the opening and the interior cavity; afirst stage valve carried within the interior cavity; a second stagevalve comprising an enlarged head carried within the opening and a shaftextending from said enlarged head within the passageway to the interiorcavity; and a coupling member coupling said first stage valve to saidshaft.
 13. The PRV assembly of claim 12 further comprising at least onebiasing member between said enlarged head and said first stage valve.14. The PRV assembly of claim 13 wherein said at least one biasingmember comprises at least one coil spring.
 15. The PRV assembly of claim12 wherein said shaft comprises a threaded shaft; and wherein said PRVassembly further comprises a threaded nut threadably engaging saidthreaded shaft.
 16. The PRV assembly of claim 15 further comprising afirst biasing member between said enlarged head and said threaded nutand a second biasing member between said threaded nut and said firststage valve.
 17. The PRV assembly of claim 12 wherein said housing hasan orifice therein from the interior cavity to an exterior of thehousing; and wherein said first stage valve comprises a first stagevalve body and a seal carried by said first stage valve body to sealablyengage adjacent portions of the housing within the interior cavity torestrict fluid communication between the interior cavity and theorifice.
 18. The PRV assembly of claim 12 wherein said first stage valvecomprises a first stage valve body having a first opening therein toreceive said shaft therein.
 19. The PRV assembly of claim 17 whereinsaid shaft has a shaft opening therein adjacent a distal end thereof;and wherein said first stage valve body has a second opening thereintransverse to the first opening and aligned with the shaft opening toreceive said coupling body therethrough.
 20. The PRV assembly of claim12 wherein said coupling body comprises a locking pin.
 21. The PRVassembly of claim 12 wherein said second stage valve comprises a sealcarried by said enlarged head to sealably engage adjacent portions ofthe housing within the opening restrict fluid communication between theopening and the passageway.
 22. The PRV assembly of claim 12 whereinsaid housing comprises first and second nested housings.
 23. The PRVassembly of claim 22 further comprising a housing seal between saidfirst and second nested housings.
 24. A pressure relief valve (PRV)assembly comprising: a housing having an opening therein, an interiorcavity, a passageway extending between the opening and the interiorcavity, and an orifice extending between the interior cavity and anexterior of said housing; a first stage valve carried within theinterior cavity to sealably engage adjacent portions of said housewithin the interior cavity to restrict fluid communication between theinterior cavity and the orifice; a second stage valve comprising anenlarged head carried within the opening and a shaft extending from saidenlarged head within the passageway to the interior cavity, saidenlarged head to sealably engage adjacent portions of said housingwithin the opening to restrict fluid communication between the openingand the passageway; a coupling member coupling said first stage valve tosaid shaft; and at least one biasing member between said enlarged headand said first stage valve.
 25. The PRV assembly of claim 24 whereinsaid at least one biasing member comprises at least one coil spring. 26.The PRV assembly of claim 24 wherein said shaft comprises a threadedshaft; and wherein said PRV assembly further comprises a threaded nutthreadably engaging said threaded shaft.
 27. The PRV assembly of claim26 further comprising a first biasing member between said enlarged headand said threaded nut and a second biasing member between said threadednut and said first stage valve.
 28. The PRV assembly of claim 24 whereinsaid first stage valve comprises a first stage valve body and a sealcarried by said first stage valve body to sealably engage the adjacentportions of the housing within the interior cavity to restrict the fluidcommunication between the interior cavity and the orifice.
 29. The PRVassembly of claim 24 wherein said first stage valve comprises a firststage valve body having a first opening therein to receive said shafttherein.
 30. The PRV assembly of claim 29 wherein said shaft has a shaftopening therein adjacent a distal end thereof; and wherein said firststage valve body has a second opening therein transverse to the firstopening and aligned with the shaft opening to receive said coupling bodytherethrough.
 31. A method of making a pressure relief valve (PRV)assembly comprising: positioning a first stage valve within the interiorcavity of a housing having an opening therein and a passageway extendingbetween the opening and the interior cavity; positioning a second stagevalve within the opening, the second stage valve comprising an enlargedhead within the opening and a shaft extending from the enlarged headwithin the passageway to the interior cavity; and coupling, via acoupling member the first stage valve to the shaft.
 32. The method ofclaim 31 further comprising positioning at least one biasing memberbetween the enlarged head and the first stage valve.
 33. The method ofclaim 31 wherein the shaft comprises a threaded shaft; wherein the PRVassembly further comprises a threaded nut threadably engaging thethreaded shaft; and wherein the method further comprises coupling afirst biasing member between the enlarged head and the threaded nut, andcoupling a second biasing member between the threaded nut and the firststage valve.